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Solar water splitting has attained much attention in recent years for renewable and clean production of hydrogen from water under irradiation by sunlight. Solar water splitting has been progressively at the forefront of chemical research and also provides a promising path for sustainable hydrogen production. TiO₂ has a wide range of applications and is considered as one of the most propitious semiconductors due to its photo-stability, low price and chemical stability. TiO₂ nanotubes have been prepared by using electrochemical anodization method followed by organic dye deposited onto the TiO₂ nanotubes. rGO-supported TiO₂ nanotubes and dye-doped graphene-supported TiO₂ nanotubes show more efficient behavior for water splitting as compared to pure TiO₂ nanotubes. The surface morphology, elemental composition, structure and size of the nanocrystalline TiO₂ nanotubes and dye-doped graphene-supported TiO₂ nanotubes were examined by using SEM, XRD, EDX and UV/Visible spectroscopy, respectively. Dye-doped graphene-supported TiO₂ nanotubes have been utilized for efficient solar water splitting.

Self-organized TiO₂ nanotubes/titanium substrate modified with palladium nanoparticles (Pd/TiO₂/Ti electrodes) were prepared by a two-step process consisting of anodizing of titanium plate followed by electroless plating of palladium on resulted TiO₂ nanotubes. The morphology and surface analysis of Pd/TiO₂/Ti electrodes were investigated using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX), respectively. The results indicated that palladium nanoparticles were homogeneously deposited on the surface of TiO₂ nanotubes. The electro-catalytic activity of Pd/TiO₂/Ti electrodes in the methanol electro-oxidation was studied by cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) methods. The results indicate that Pd/TiO₂/Ti electrode improve the electro-catalytic activity for methanol oxidation greatly and confirmed the better electro-catalytic activity and stability of these new electrodes. So, the Pd/TiO₂/Ti electrodes have a good application potential to fuel cells.

C-doped TiO₂ nanotubes (NTs) with anatase structure, prepared by anodizing the polished Ti foils, were characterized using X-ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM), and synchrotron-based X-ray photoemission spectroscopy (XPS). XPS results show electron losses in C atoms, no electron change in Ti atoms, and two doping energy levels appeared in band gaps. Structural geometries, DOSs, PDOSs, and Bader charge analyses of C-doped TiO₂ anatase are predicted by periodic DFT calculations. Eight doping positions were taken into consideration: two substitutional cases (in oxygen and titanium sites) and six interstitial cases. We found that the interstitial carbon doping type is the most stable one, whereas the substitutional cases are rather unstable. Band-gap modifications can also be found in oxygen substitution, but not in titanium substitution. Both band-gap modification and non-band-gap modification are found in the interstitial carbon doping. In these eight C-doping systems, only the C atom in the oxygen substitution case gains electrons, 1.14 e, and others present electron losses within 0.5–4.00 e. The results of XPS measurements, DOSs calculations, and Bader charge analyses show that carbon interstitial is the most likely doping type for the C-doped TiO₂ NTs.

Zinc oxide (ZnO) nanorods (NRs) have been synthesized as a template to fabricate TiO₂ nanotubes (TiNTs) on hemispherical diamond film by liquid-phase deposition (LPD) method. The process concerning the formation of TiNTs was analyzed. Based on the results of XRD and Raman spectroscopy, it is demonstrated that TiNTs was successfully obtained after removing ZnO NRs by chemical etching at room temperature. The TiNTs on hemispherical diamond film show higher performance photocatalysis, examined by the degradation of the reactive yellow 15 (RY15) solution. The corresponding mechanism is discussed.

Ruthenium (II) polypyridyl complexes modified titanium dioxide materials with anatase phase, the length of 10–100nm, were synthesized by a hydrothermal method. Photocatalytic CO₂ reduction experiments were performed in sensitized TiO₂ aqueous suspensions under UV–Vis light in closed systems. And only methanol was detected in the liquid phase under the experiment condition. The effect of different photosensitizers content on the photoactivity of TiO₂ was also studied, showing that Ru(BiDiPy)₂(NCS)₂ sensitized TiO₂ was the optimal photocatalyst in transformation of CO₂ to methanol. A possible mechanism for the photocatalytic reduction was also proposed in this paper.

By adjusting the oxidation voltage, electrolyte, anodizing time and other parameters, TiO₂ nanotubes with high aspect ratio can be prepared by oxidation in organic system because anodic oxidation method has the advantage of simple preparation process, low material cost and controllable morphology. This review focusses on the influence of anodizing parameters on the morphology of TiO₂ nanotube arrays prepared by anodizing. In order to improve the photocatalytic activity of TiO₂ nanotubes under visible light and to prolong the life of photo-generated carriers, the research status of improving the photocatalytic activity of TiO₂ nanotubes in recent years is reviewed. This review focusses on the preparation and modification of TiO₂ nanotubes by anodic oxidation, which is helpful to understand the best structure of TiO₂ nanotubes and the appropriate modification methods, thus guiding the application of TiO₂ nanotubes in practical photocatalysis. Finally, the development of TiO₂ nanotubes is prospected.

Continuously increasing atmospheric concentrations of CO₂ have given rise to great concerns about climate change. Photocatalytic reduction of CO₂ to chemicals by solar energy is considered a green and sustainable process. Interactions between CO₂ molecules and photocatalysts surfaces are the key factors that affect photocatalytic reduction efficiency. Thus, a better understanding of their reactive species on the TiO₂ nanotube (TNT) surfaces by in situ FTIR spectroscopy was studied in the present work. The FTIR absorbance features at 1303cm${}^{-1}$ and 1393cm${}^{-1}$ were associated with carbonate species, e.g., bidentate carbonate on the TNT. Complete desorption of CO₂ from the TNT occurred at $T>418$K. The carboxylate species that were adsorbed on the TNT may conduct the surface reactions enhanced by UV–Vis light to yield low carbon chemicals.

TiO₂ is a promising photocatalyst in the reaction of water splitting for hydrogen. Here, we used NaBH₄ reduction reaction to introduce ${\text{Ti}}^{3+}$/V_O defect states into Si-doped TiO₂ nanotubes and investigated the photoelectrochemical water splitting properties. It was found that the photocatalytic activity was improved through NaBH₄ reduction because of the existence of ${\text{Ti}}^{3+}$/V_O. The defect states (${\text{Ti}}^{3+}$/V_O) could play a role of capture trap and accelerate the separation of photogenerated electrons and holes. The photocurrent density of the Si-doped TiO₂ nanotubes reduced for 3h was 1.5mA/cm² compared to 0.7mA/cm² of the unreduced nanotubes. The conversion efficiency was 0.7%, which was almost 4 times than that of pure TiO₂. On the other hand, reduction for a long time would generate excess defect states and thus cause the decrease of photocurrent density. Excess defect states could act as the recombination centers of photogenerated electrons and holes.

The rechargeable lithium-sulfur batteries were investigated as the most promising energy storage system. Although the composites of carbonaceous materials and metal oxides as the hosts of sulfur have been applied to improve the performance, their structures usually collapsed due to huge volumetric expansion of sulfur. Therefore, interlayer reported as a novel cell configuration could efficiently restrict the shuttle effect of polysulfide. Here, we design a unique separator modified by a functional “polysulfide trapping net” which consists of intertwined TiO₂ nanotubes and carbon nanotubes to improve the electrochemical performance of lithium sulfur batteries. Benefiting from the network structure, there are abundant ion pathways, meanwhile, TiO₂ nanotubes provide strong chemical and physical adsorption, carbon nanotubes serve as a conductive network which accelerates the transport of electrons. With the modified separator, the electrode exhibits an initial capacity of 936mAhg${}^{-1}$ at 1C rate and maintains a stable cycling performance over 200 cycles.

The morphology, composition and the electrochemical behavior of the anodic nanoporous layer, prepared by the galvanostatic anodisation of titanium, followed by galvanostatic deposition of noble metal particles have been investigated. The morphology and surface characteristics of result electrodes were investigated using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX), respectively. The results indicated that noble metal particles were homogeneously deposited on the surface of TiO₂ nanotubes. The nanotubular TiO₂ layers consist of individual tubes of about 40-80 nm diameters. The electrocatalytic behavior of result electrodes for electro-oxidation of organic compounds (glucose, dopamine, ascorbic acid and hydrazine) was studied by cyclic voltammetry. The results showed that the result electrodes possess catalytic activity toward the oxidation organic compounds.